Electrical contact and method of making the same



Nov. 22, 1538. R, 'H' MEs ET AL 2,137,617

ELECTRICAL CONTACT METHOD OF MAKING THE SAME Filed March 4, 1936 I k '4INVENTQRS jwm ,9, [W5 f/ l Ffzfa/k TTORNEY Patented Nov 22, 1938 7 i 4UNITED STATES PATENT OFFlCE ELECTRICAL CONTACT AND METHOD OF MAKING THESAME Robert 11. lines and Hal F. Fruth, Indianapolis,

Ind., asdgnors to P. R. Mallory & 00., Inc., Indianapolis, Ind.,avcorporation of Delaware Application March 4, 1936, Serial No. 67,010

13 Claims. (01. 29-15555) This invention relates to electrical contactscontacts wherein a contact face of silver or a.

and methods of making the same. silver alloy is integrally united to asteel backing. An object of the invention is to improve the In priorpractice such contacts have been made methods of making electricalcontacts. by punching the contact discs out of bimetallic Another objectis to produce an improved elecsheet stock consisting of a sheet of steelhavin 5 trical contact. a uniform layer of silver welded to its surface.Other objects of the invention will be appar- It will be readilyapparent that this procedure ent from the following description andaccomis wasteful and uneconomical because of the panying drawing takenin connection with the fact that a sizeable proportion of the silver isappended claims. left onthescrap material from which the con- 10 Theinvention comprises the features of contact discs have been punched.These prior struction, combination of elements, arrangemethods,therefore, require a considerable inment of parts, and methods ofmanufacture and vestment in material which is converted into operationreferred to above or which will be scrap which requires furtherprocessing in order brought out and exemplified in the disclosure torecover the precious metal; The present ill-'15 hereinafter set forth,including the illustrations vention provides an improved method ofmaking in the drawing, the scope of the invention being contacts whichdoes not have these objections.

indicated in the appended claims. Referring to the drawing, asilver-faced con- For a fuller understanding of the nature and fact i0is illustrated in Figures 1 and -2 and the objects of the invention aswell as for specific method of making the contact is illustrated in 0fulfillment thereof, reference should be had to Figures 3 to 8. In thismethod a strip .of sheet the following detailed description taken inconsteel II is run through a stamping machine or nection with theaccompanying drawing in punch press wherein a series of annular grooveswhich: 12 are stamped in the strip. In the same opera Figure 1 is a faceview of an electrical contact tion an indentation I3 is formed on thesame 25 made according to the present invention; face with the annulargroove and preferably Figure 2 is a section on the line 2-2 ofFigconcentric therewith. A corresponding projecure 1; tion 14 is therebyprovided on the opposite face Figure 3 is a face view of a steel blankus d in ofthe strip. A series of locating or centering fabricatingcontacts of the kind shown in Figholes i 5 is also punched in the stripin a line 30 ure 1; parallel to the line of centers of the annularFigure 4 is a section on the line H of Figgrooves, the centering holesbeing spaced apart ure 3; I by the same distances as the annulargrooves. Figure 5 is a section through a preliminary After the aboveoperation the steel strip will have 85 assembly comprising the steelblank and a disc the form Shown in Figures 3 and of contact metal; Thenext step in the procedure is to place Figure 6 is a section through theassembly a piece It of the contact metal, such as silver, after fusionof the contact metal to the steel on or in contact with the steel stripwithin the backing; area enclosed by each annular groove l2. The

Figure 7 shows the coining operation; nd pieces each contain a definitepredetermined 4.0

gure 8 shows the operation of punching th quantity of metal and may bein the form of discs contact from the steel strip on which t was punchedfrom sheet, slugs punched from wire formed. or small pieces formed inother ways.

While a preferred embodiment of the inv nti The steel strip ll, carryingpieces iii in con- 5 is described herein, it is contemplated th t tact,is then passed through a'furnace where siderable variation may be madein th m th d the assembly is heated to a temperature above of procedureand the construction of parts iththe melting point of the silver orsilver alloy. ut. departing from th Spirit 0f t invention When thesilver is in the molten condition it flows In the following descriptionand in the clai out over the surface of steel strip H until it Partswill be identified by specific names fo reaches-the inner edge of groovel2, where the 50 convenience, but they are intended to be as is d, p a ya e the Surface generic in their application to similar pa t as tensionof the molten silver is greater than the the art will permit. attractionof the silver for the steel at this point. An important use of thepresent invention is Should the silver flow over the inner edge of 56 inthe production of steel-backed silver-faced the groove it will bestopped at the outer edge.

' the edges thereof.

There results a body of molten silver which solidifies, on removal fromthe furnace, into a solidlayer l'l adhering to the steel backing withinthe area bounded bythe annular groove, the silver layer having a convexcircular face l8 (Fig. 6).

The convex face l'l may, in some instances, be suitable for use as acontact face without extra treatment. It is generally desirable,however, to insure perfect uniformityof dimensions and to obtain theexact radius of curvature desired, to coin the surface. This isaccomplished, as indicated in Figure '7, by a pair of punches l9 and 20held. in a suitable pressing arrangement. Punch l9 has a face shaped toreceive the projection It on the back of the strip and punch 20 has aface 30 of the curvature necessary to apply the desired radius 21 to thesilver face. In the coining operation the contact can be centered withrespect to the punches by one or more locating pins 22 adapted to fitinto holes I5.

The finished contacts are punched from strip II by a punch 23, having aface shaped to receive projection 14, in cooperation with a die 24. Thepunch 23 and die 24 have a diameter 26 slightly less than that ofannular ring 12 so that some of the silver contact metal is drawn downaround the sides of the punched disc to cover the edges as is apparentfrom Figure 2. In the punching operation locating pin 25 co-operateswith hole I5 in the steel strip to center the contact in the die.

The finished contact I0 is thereby produced having a circular silverface with a curvature 2|, the silver face being integrally attached to asteel backing disc 21 and extending down over The steel disc 21 also haswelding projection l4 whereby the contact can be electrically welded toa switch spring, circuit breaker armature, breaker arm, relay armatureor any other metal part on which it is desired to provide contacts.

It will be obvious that other contact materials, in some instances, canbe used in place of silver and other backing materials can be used inplace of steel. Composite facings may also be formed. The metal incontact with the backing must, of course, be of lower melting point thanthe backing metal.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. The method of making an electric contact which comprises providing anannular groove in one face of a sheet of backing metal, placing aquantity of lower melting point contact metal in contact with said facein the area surrounded by said groove, heating the assembly thusproduced to a temperature above the melting point of said contact metal,whereby itis fused to said backing metal, cooling said assembly andpunching a disc from an area of said backing metal sheet including atleast part of the area within said annular groove, said groove servingto limit the flow of the melted contact metal during said heating.

2.-The method of making an electric contact which comprises providing agroove in one face of a backing metal member, said groove enclosing aportion of the area of said surface, placing contact metal of lowermelting point than said backing metal against said portion, heating saidassembly above the melting point of said contact metal but below themelting point of said backing metal, and cooling the integral assemblythus produced, said groove serving to limit the flow of the meltedcontact metal during said heating.

3. The method of making an electric contact which comprises providing agroove in one face of a metal backing member, said groove enclosing aportion of the area of said face so as to prevent the flow of moltenmetal of lower melting point than the backing metal away from said area,placing facing metal in contact with said area, at least a portion ofsaid facing metal being suitable for a contact facing and at least aportion of said facing metal being of lower melting point than saidbacking metal, heating the assembly thus produced above the meltingpoint of said lower melting point metal but below the melting point ofsaid backing metal whereby said lower melting metal will fuse to thesurface of said backing metal within said area, and cooling the integralassembly thus produced.

4. The method of making an electrical contact assembly which comprisesforming a moat in a face of a backing metal member, placing a lowermelting metal in contact with said face inside said moat, heating tofuse said lower melting metal and cooling to solidify the integralassembly thus produced, said moat serving to limit the flow of themelted contact metal during said heating.

5. The method of making an electrical contact which comprises stamping acircular groove in a face of a backing metal member, placing a piece ofcontact metal of lower melting point than said backing metal within thearea enclosed by said groove, heating the assembly to a temperature highenough to melt said lower melting metal only, and cooling the integralassembly thus produced, said groove serving to limit the fiow of themelted contact metal during said heating.

6. The method of making an electrical contact which comprises stamping amoat in a face of a backing metal member, placing a piece of silvermetal within the area enclosed by said moat, heating the assemblysufliciently to fuse said silver metal without fusing said backingmetal, then cooling the assembly below the melting point of said silvermetal, said moat serving to limit theflow of the fused silver metalduring said heating.

7. The method of making an electrical contact which comprises stamping acircular groove on one face of a piece of sheet steel, placing a pieceof silver metal within the area enclosed by said groove, and heating theassembly to fuse the silver to the steel, said groove serving to limitthe flow of the fused silver metal during said heating.

8. The method of making an electrical contact which comprises stamping acircular groove on one face of a piece of sheet steel and raising awelding projection on the other face opposite the area enclosed by saidcircular groove, placing a quantity of silver in contact with the areaenclosed by the circular groove, heating the assembly sufllciently tofuse said silver to said area and cooling the integral assembly thusproduced, said groove serving to limit the flow of the fused silverduring said heating.

9. The method of making an electrical contact which comprises stamping acircular groove on one face of a piece of sheet backing metal, fusing abody of silver metal to said face within the area enclosed by saidgroove, and punching a bi-metal disc from the silver-backing metalassembly, said groove serving to limit the flow of the fused silvermetal during said heating.

10. The method of making an electrical contact which comprises stampinga circular groove on one face of a piece of sheet backing metal, fusinga body of silver metal to said face within the areaenclosed by saidgroove, coining a contact face on said silver metal and punching abimetal contact from the assembly, said groove serving to limit the flowof said silver metal during fusing.

11. The method of making an electrical contact which comprises stampinga circular grooveon one face of a piece of sheet steel, raising awelding projection on the other face of said sheet opposite the areaenclosed bysaid groove, fusing a body of silver metal to said facewithin the area enclosed by said groove, coining a contact face onsaid'silver metal and punching a bi-metaicontact disc from an areaincluding said silver and said welding projection, said groove servingto limit the flow of said'silver metal during fusing. v

12. A blank for producing a contact backing comprising a strip of sheetmetal having a row of locating holes punched therein, said row being ona line parallel to one edge of said strip, said strip also having a rowof annularly grooved portions parallel .to said holes.

13. The method of making a bimetal electric contact disk having a curvededge, without wastage of the contactmetal facing, which comprisesintegrally securing a layer of contact metal to a sheet metal backing inan area correspondingto an i ndividual contact surrounded by an area ofbacking metal substantially free from contact metal and thenpunchingsaid bimetal contact disc out of said sheet metal backing bysevering said backing along a line substantially at the boundary of thearea to which said contact metal is secured and simultaneously drawingsaid contact'metal down over the edgeof the backing along the curvededge of said disc thereby to produce said bimetal contact having a.

curved edge and with the entire face'and edge thereof covered withcontact metal.

Roam-ram." mrumu'rn.

